Scapulohumeral rhythm benefits include preserving what?

• A. It preserves joint spaces and maintains congruity
• B. It reduces shoulder stability
• C. It increases impingement risk
• D. It has no impact on motion

Answer: (A)

When the arm lifts, the shoulder relies on a coordinated movement between the scapula and the humerus. This scapulohumeral rhythm keeps the joints in proper alignment so there is adequate space between moving parts and the joint surfaces stay congruent. As the humerus elevates, the scapula upwardly tilts, rotates, and tilts posteriorly, creating a harmonious 2:1 rhythm that preserves the subacromial space and prevents the humeral head from jamming under the acromion. This helps maintain the relationship of the glenohumeral joint surfaces and distributes loads so the joint surfaces remain aligned and surfaces stay in contact smoothly, preserving joint spaces and congruity throughout shoulder elevation. If this rhythm is off, the space under the acromion can narrow, increasing impingement risk and compromising smooth articulation.